Structural and Cellular Changes in the Mouse Thymus During Pregnancy

Abstract

During pregnancy in all mammals, including man, there is a massive loss of lymphocytes from the thymus. This is reflected in an excessive involution, with decreases in weight and in the numbers of thymocytes. At the end of pregnancy in the mouse, the thymus has lost 75% of its weight and cells. Involution continues during lactation, after which the thymus regenerates, becomes repopulated with lymphocytes, and regains its original size.